I got the internal battery out of my Simrad CX34. It was as far inside the unit as possible, requiring removal
of the screen
, a layer of circuits and the motherboard, and of course a soldering iron to get it off the board. Then I went looking for a replacement. The only place I could find a similar battery (same battery, different pins) wanted to sell me a USED one with a manufacturing date of ten years ago (he didn't realize that the month and year were on the thing).
When I bought my boat I had "Cheat me" tattooed to my forehead.
I ordered a battery online. Less than $10 including shipping